Contrasting response to Pleistocene climate change by ground-living and arborealMandarinasnails from the oceanic Hahajima archipelago

Abstract

While the genetic impact of Pleistocene climate change on temperate species has been well characterized, especially in Europe and North America, an effect on the diversification of species on oceanic islands has been less well studied. This is perhaps a surprising observation given the traditional and continuing contribution of island species (e.g. Darwin's finches, Partula snails, Lord Howe Island palms) to understand speciation. Here, we combine mitochondrial and microsatellite data from the ground-living and arboreal Mandarina snails of the oceanic, subtropical Hahajima archipelago (Ogasawara, colloquially 'Galápagos of the Orient') to enable a comparative approach to understand the impact of the Pleistocene glaciations on their phylogeography. Prior work suggested that several narrowly divergent, ground-living species pairs of Mandarina populations on the outlying islands, as well as the low-lying southern and central parts of Hahajima, probably underwent bottlenecks and subsequent expansions during the recent Pleistocene. Here, the most striking finding is that largely arboreal species have deeply divergent, geographically restricted mitochondrial lineages, in contrast to a census size that is at least an order of magnitude lower than ground-living snails. As populations of both types are highly polymorphic at microsatellite loci, the systematic difference at the mitochondrial locus probably indicates a contrasting effect of the Pleistocene climate cycles on the two groups. We speculate that this may have partly come about owing to a reduced efficacy of natural selection on the more greatly structured populations of arboreal snails. If so, then a prediction is that the genome of other snails, or other species with limited mobility, will show a similar response to the Pleistocene climate cycles.

Tropical mountain passes are out of reach – but not for arboreal species

“…A scattered but growing literature has emerged in support of the relationship between ecological and physiological processes and arboreal lifestyles. Our results suggest that arboreal species should be able to tolerate differences in temperature across time and/or space with consequences on both opposing fronts of biogeography: (1) species diversification versus (2) species resilience and likelihood of extinction due to environmental instability (Davison and Chiba ; Scheffers et al . ).…”

“…For instance, Thompson () observed a geographic gradient of decreasing climbing ability in Peromyscus deer mice from the US Southwest as forested woodlands (high climbing ability) transitioned to desert grasslands (low climbing ability). Likewise, a genetic analysis of ground‐dwelling and arboreal Mandarina snails from southern Japan (Davison and Chiba ) demonstrates how tree‐living influenced paleoecological processes. The ground‐living snails experienced a population bottleneck and loss of genetic variation (founder event) during the Pleistocene glaciations, whereas tree‐living snails maintained isolated but stable populations and therefore generated clearly divergent lineages and exhibited mitochondrial genetic diversity during the same period of time.…”

Divergence before and after the isolation of islands: Phylogeography of the Bradybaena land snails on the Ryukyu Islands of Japan

“…If the results of the 16S clock rate are correct, this vicariance‐based view is supported. However, Davison and Chiba () showed that the evolutionary rate of mtDNA (16S) of Mandarina changes depending on the population structure. The evolutionary rate of mtDNA is likely to be accelerated in small and isolated populations, like those often found on oceanic islands, rather than in large populations of widely distributed lineages such as Bradybaena .…”

Vertical stratification influences global patterns of biodiversity

“…Second, verticality infers greater persistence to climatic instability (Davison and Chiba 2008, Scheffers et al 2013, Scheffers and Williams 2018. Vertical movements, either upwards in the canopy or downwards into the ground, afford more plastic ecologies and confer advantages over entirely ground-dwelling species due to a greater accessibility to micro-habitats and climates.…”